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Serotonin-depleting midbrain lesions do not prevent ovariectomy-induced weight gain
1Section of Biopsychology, Clarke Institute of Psychiatry, Toronto, Ontario, Canada.
Abstract:
Past research has shown that subdiaphragmatic vagotomy and midbrain raphe lesions are each effective in impeding the development of hypothalamic obesity while neither affects the development of genetic obesity in Zucker rats. To further test the parallels that may exist between these two manipulations on another putative obesity model, we studied the effects of midbrain raphe lesions on the development of ovariectomy-induced weight gain, previously shown to be unaffected by vagotomy. Ten adult female rats received thermal lesions of the dorsal and median raphe nuclei (RAPHE) while 7 served as sham controls (SHAM). Following a 26-day recovery period during which body weight, food intake and water intake were periodically monitored, bilateral ovariectomy (OVX) was performed on 7 RAPHEs and 4 SHAMs, with laparotomy (LAP) being performed on 3 RAPHEs and 3 SHAMs. Body weights and intake variables were monitored for an additional 58 days, then animals were sacrificed for brain histological and biochemical assessments. RAPHEs weighed less despite eating and drinking more than SHAMs throughout this study. Nevertheless, OVX rats gained more weight regardless of lesion (mean +/- SEM weight gain = 73.9 +/- 5.5 g for RAPHE + OVX and 67.0 +/- 6.6 g for SHAM + OVX vs. 30.7 +/- 3.0 g for RAPHE + LAP and 39.7 +/- 5.5 g for SHAM + LAP). This occurred without reliable changes in the food or water intakes of either OVX subgroup. Histology confirmed that RAPHE lesions were largely localized to the dorsal and median raphe nuclei, as planned.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Midbrain raphe lesions did not prevent ovariectomy-induced weight gain in rats, suggesting this obesity model differs from hypothalamic obesity and is not affected by raphe nucleus manipulation.
Area of Science:
- Neuroscience
- Endocrinology
- Obesity Research
Background:
- Subdiaphragmatic vagotomy and midbrain raphe lesions impede hypothalamic obesity but not genetic obesity in rats.
- Ovariectomy induces weight gain, a model previously unaffected by vagotomy.
Purpose of the Study:
- To investigate the effect of midbrain raphe lesions on ovariectomy-induced weight gain.
- To compare the impact of raphe lesions on this obesity model with their known effects on hypothalamic obesity.
Main Methods:
- Adult female rats received thermal lesions of the dorsal and median raphe nuclei (RAPHE) or sham procedures (SHAM).
- Following recovery, rats underwent bilateral ovariectomy (OVX) or laparotomy (LAP).
- Body weight, food intake, and water intake were monitored throughout the study; brain histology confirmed lesion accuracy.
Main Results:
- Raphe-lesioned rats weighed less but consumed more food and water than sham controls.
- Ovariectomy significantly increased weight gain in both lesioned and sham-operated rats.
- Weight gain in ovariectomy groups occurred without significant changes in food or water intake.
Conclusions:
- Midbrain raphe lesions do not prevent ovariectomy-induced weight gain in female rats.
- This finding indicates that the mechanisms underlying ovariectomy-induced obesity differ from those in hypothalamic obesity models.
- The raphe nuclei's role in regulating body weight may be specific to certain obesity etiologies.